The present invention concerns methods of making integrated circuits, particularly layer-formation methods, such as chemical vapor deposition.
Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators generally build the circuits layer by layer, using techniques, such as deposition, doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
One common technique for forming layers in an integrated circuit is called chemical vapor deposition. Chemical vapor deposition, or CVD, generally entails placing a substrate in a reaction chamber, introducing one or more gases, known as precursor gases, into the chamber, and heating the substrate to prescribed temperatures. The precursor gases enters the chamber through a gas-dispersion fixture, such as a gas ring or a showerhead, one or more centimeters above the substrate and descend toward the heated substrate. The gases react with each other and/or the heated substrate, blanketing its surface with a layer of material having a composition based on the gases.
Because of demands for smaller and smaller integrated circuits, it has become increasingly important that layers, such as those made using chemical vapor deposition, have uniform thickness across the substrate. One method of promoting uniform thickness in chemical vapor depositions is to coat the gas-dispersion fixture with a uniform layer of the material before using the fixture in an actual deposition on a substrate. This method is generally known as conditioning. Conventional conditioning techniques entail running the CVD chamber through several normal deposition cycles (that is, at normal temperatures and pressures) on a test or dummy substrate before using it for actual fabrication.
However, this conventional conditioning technique suffers from at least three problems. First, this technique produces coatings of poor thickness uniformity across gas-dispersion fixtures. In operation, these unevenly coated fixtures disperse gas unevenly and produce uneven depositions. Second, for large fabrication plants with many ideally identical CVD chambers, the coatings vary significantly from fixture to fixture, making it difficult for the CVD chambers to deposit layers of consistent quality. And third, the conventional technique yields coatings that adhere poorly to the gas-dispersion fixtures. Particles from poorly adherent coatings sometimes fall from fixtures onto underlying substrates, causing defects in integrated circuits.
Accordingly, there is a need for better ways of coating or conditioning gas-dispersion fixtures to promote uniform chemical vapor deposition and/or to reduce defects in integrated circuits.
To address these and other problems, the present inventors devised new procedures for conditioning gas-dispersion fixtures in chemical-vapor-deposition (CVD) chambers. One conditioning procedure, in accord with the invention, entails heating at least a portion of a gas-dispersion fixture, such as a showerhead, to a temperature greater than its temperature during normal deposition operations and then passing one or more gases through the fixture to form a coating on it. Exemplary methods for raising the fixture temperature beyond its normal level include placing the fixture closer to a heated substrate holder than its normal operating position and/or introducing high-powered plasma in the vicinity of the fixture.
Increasing the temperature of the fixture during conditioning promotes uniform coating thickness and coating adhesion to the fixture. These in turn promote uniform chemical vapor depositions and reduce the likelihood of coating particles falling onto underlying substrates and causing integrated-circuit defects.
Other aspects of the invention include conditioning a gas-dispersion fixture at a higher-than-normal temperature, reducing the gas-dispersion fixture temperature, and then using the gas-dispersion fixture at the reduced temperature to form a layer of an integrated circuit.